Impact of sodium ion on multivalent metal ion content in extracellular polymeric substances of granular sludge from an expanded granular sludge bed.

The long-term and short-term effects of salinity on the multivalent metal ions within extracellular polymeric substance (EPS) were investigated in this study. The results indicated that the Na content within the EPS increased significantly from 19.53% to 60.86% under high salinity, and this content in the saline system was 2.2 times higher than that of the control system at the end of the operation. The K, Ca and Mg contents within the EPS decreased from 33.85%, 39.19% and 5.54% to 7.07%, 25.64% and 3.28%, respectively, when the salinity was increased from 0 g/L to 30 g/L. These ions were replaced by Na through ion exchange and competing ionic binding sites under salt stress. The interaction between divalent metal ions and Na was reversible with the adaption of anammox to salinity. Salinity exhibited a limited influence on the Fe within the EPS. Sludge granulation was inhibited under conditions of high salinity due to the replacement of multivalent metal ions by Na.